Hi! My name is Yitian, and I am a gold medalist from the 2021 IChO hosted by Japan. Here’s some of the free resources I found helpful:
This is a student-run organization committed to helping people study. Previous Study Camp and IChO participants write Mock Exams of all levels, and they host informal mock tournaments. I found their practice tests and tournaments the most helpful.
Edward’s and Anugrah’s websites: http://www.mit.edu/~ehjin/chem.html , http://www.mit.edu/~anugrah/chem.html
These websites contain practice exams and resources created by my great friends Edward and Anugrah. They were IChO gold medalists as well and were mentors at the study camp in 2021.